The sliding friction and wear of silicon nitride was investigated in 600 deg C air using a ball-on-disk configuration. Two cesium-based inorganic films were studied as potential high-temperature solid lubricants for limited-life turbine engine bearing applications: a sodium silicate bonded Cs2WOS3 coating and a cesium silicate chemical reaction film. Wear surfaces were characterized using various analytical techniques. The best tribological performance was obtained with thin chemical reaction films annealed in sulfur-rich air. Friction coefficients (f) and wear factors as low as 0.04 and 4 x 10(exp -9) cu mm/N.m respectively, were obtained at 600 deg C with this system. These are comparable to boundary liquid lubricating films at much lower temperatures. The data provide conclusive evidence that neither tungsten nor molybdenum is necessary for low friction at 600 deg C. The results also suggest that sulfur and cesium play important roles in the formation of a lubricious silicate film by chemically reacting with the silicon dioxide scale that naturally forms on silicon nitride surfaces. This occurs via a complex hot-corrosion mechanism involving the inward diffusion of oxygen from the surrounding air and cesium from the coatings and the outward diffusion of nitrogen and magnesium from the silicon nitride substrate. It is believed that sulfur provides a reaction path for the hot-corrosion mechanism.